Deep-water Sea Research Articles

Iceberg ploughmarks and glacial lineations on Jan Mayen Ridge: Evidence for past iceberg and possible ice-shelf grounding in deep water

Jan Mayen Ridge, south of the isolated island of Jan Mayen (71°N 8°W), is located strategically near the centre of the Polar North Atlantic and surrounded by deep-water seas. Examination of about 4,100 km2 of multibeam bathymetric data allowed identification of 1700 chaotic seafloor depressions at 300–1000 m modern water depth and two sets of lineations at 400–600 m and 750–900 m deep. The chaotic depressions are interpreted as ploughmarks produced as iceberg keels impinged on a sedimentary seafloor. The deepest ploughmarks reach 1010 m depth. Multi-keel ploughmarks indicate the presence of tabular icebergs of minimum widths 0.5–2.3 km. Ploughmark orientations were W/E and SW/NE on the northern and southern ridge, respectively, suggesting that deep-keeled icebergs drifting across Jan Mayen Ridge were probably calved mainly from short floating tongues at the margins of full-glacial Greenland ice streams. The mapped seafloor lineations are morphologically similar to mega-scale glacial lineations and flutes formed by soft-sediment deformation beneath active ice. They are interpreted to indicate the possible grounding of glacier ice on Jan Mayen Ridge. Their W-E orientation precludes ice flow from a full-glacial Jan Mayen ice cap. A possible interpretation is that they may represent grounding of a large floating ice shelf probably fed by ice from the Greenland Ice Sheet during one of the very large pre-Weichselian glaciations of the Quaternary. Whereas these lineations at 70°N do not provide direct evidence for a huge ice-shelf complex flowing southwards from the Arctic Ocean, the general climatic conditions required to form and maintain large ice shelves suggest that the development of an Arctic Ocean ice shelf at some point during Quaternary full-glacials remains a possibility.

A novel design of multifunctional offshore floating platform structure based on topology optimization

Floating platforms are an economical option for offshore energy harvesting in deep water sea. Lightweight design and structural stability are most important concerns in the design of floating foundations under the premise of ensuring load-bearing capacity. Topology optimization has proven to be a successful method for determining the optimal material distribution with the desired stiffness, strength, and robustness of the subjected design structure. In this paper, a novel lightweight multifunctional offshore floating platform design is proposed utilizing the density-based topology optimization method for the combined utilization of wind-solar-wave energy. Firstly, based on the extreme sea conditions in the South China Sea, the minimum compliance subject to the prescribed volume percentage is formulated and an innovative platform structure is carried out by interoperating the variable density method in the ANSYS AQWA module. Secondly, the optimized floating platform structure was strength-checked based on the maximum von Mises stresses under extreme loading conditions specified in the DNV code. The total mass of the novel optimized structure is 40.82% of the primary structure. Moreover, the platform stiffness and durability have been significantly enhanced.

Hydrological characteristics of the Bering Sea in the summer of 2019

Based on the data of three CTD sections in the northern, northeastern and western Bering Sea of 2019 voyage of Chinese National Arctic Research Expedition (CHINARE), this paper analyzes and studies the hydrological characteristics of the water mass distribution, layered structure, and cline characteristics in different sea areas of the Bering Sea. The results indicate that the hydrological characteristics of the Bering Sea in the summer of 2019 are different from those in the past and that the water mass is warming in many locations. The maximum water temperature reaches 11.13 °C, and the maximum thickness of the warm water is about 32 m. The water mass composition and characteristics of the north-northeast-west sections are significantly different: the BL section has the highest salinity, while the BS section has the lowest salinity, and both the lowest temperature and the largest temperature variation appear in the BL section. The stratification characteristics in all sea areas are noteworthy. In the deep-water seas, there are three types of water masses: upper water (BSW), middle water (BIW) and deep water (BDW) from top to bottom, while two main water masses appear in the shelf waters with the Alaska Coastal Water (ACW) overlies the Bering Sea Shelf Water (BSW). Along the Bering Sea Slope Current (BSC), the water mass is essentially steady. Statically unstable hydrological inversion structure appears near the bottom of the three stations at the northern end of the BL section.

Techno-economic evaluation and resource assessment of hydrogen production through offshore wind farms: A European perspective

The demand for hydrogen is expected to increase radically in the coming years, as it is an important lever for decarbonization and offshore wind is a credible option for running electrolyzers. A unified and detailed cost modeling is produced from the sparse literature that considers a variety of configurations (onshore, centralized offshore, and decentralized offshore electrolysis). A resource assessment at European scale is performed by combining the developed cost modeling with a geospatial analysis considering the levelized cost of hydrogen (LCOH). Geolocated power generation as well as technical and environmental constraints are considered to improve the assessment.The results reveal enormous resources in European seas, with LCOH falling from 4.5–7.5 €/kg in 2020 to 1.5–3.0 €/kg in 2050 as the costs of wind turbines and electrolyzers decrease. More than 1000 TWh of green hydrogen could be produced at a price of less than 3.0 €/kg in 2030 and 2.0 €/kg in 2050, making it competitive with gray hydrogen. A valuable resource of 200 TWh is identified in 2030 where offshore wind-to-hydrogen projects have a much lower LCOH than their wind-to-power counterparts. The results, provided at the country level, are valuable for energy modelers and local stakeholders. Finally, a detailed cost analysis shows that offshore electrolysis is becoming more relevant over time: In 2020, offshore electrolysis is preferred only for far-from-shore and deepwater seas while in 2030 it is closer to shore (over 100 km). In 2050, onshore electrolysis is only relevant for nearshore and shallow waters.

Experimental Modelling of a Floating Solar Power Plant Array under Wave Forcing

Floating Photovoltaic (FPV) plants are already well developed, and deployed all over the world, on calm water inland lakes, or in sheltered locations. They are now progressing to be installed in nearshore sites, and in deep water seas. The company HelioRec, developing floating modules to form FPV arrays to be deployed in nearshore areas, was awarded free-of-charge testing of their system by the Marine Energy Alliance (MEA) European program. This paper describes the experimental testing of the 1:1 scale float system, composed of 16 floating modules supporting solar panels and three footpaths, carried out in Centrale Nantes’ ocean wave tank, allowing regular and irregular frontal and oblique wave conditions. Experimental results show that, even in the narrow wave spectrum experimentally achievable, a specific response from the array was revealed: the multibody articulated system exhibits a first-order pitch resonant mode when wavelengths are about twice the floater length. A shadowing effect, leading to smaller motions of rear floaters, is also observed, for small wavelengths only.

Characterization of Lime and Polymer Treated Ultra-Soft Clay Soils Using the Modified Vane Shear and Correlating the Shear Strengths to the Electrical Resistivity and CIGMAT Miniature Penetrometer for Nondestructive Field Tests

With the growth in construction along the coastal regions, ports and offshore deepwater sea beds, ultra soft clay soils are encountered and are affecting the performance of the pipelines and other anchor systems placed in it. In this study, untreated and treated ultra-soft clay soils shear strengths were quantified using the modified vane shear device and correlated the shear strength to the CIGMAT miniature penetrometer penetration and electrical resisitivity. The ultra-soft clay soils were prepared by varying the bentonite content from 2 to 10%. The soil with 10% bentonite was treated with 2–10% lime and with 1–10% polymer separately to enhance the shear strength. The shear strength, pH, CIGMAT miniature penetrometer and electrical resistivity were used to characterize the untreated and treated ultra-soft clay soils. Untreated soft soil strength varied from 0.01 to 0.17 kPa when the bentonite content in the ultra-soft clay soil was increased from 2 to 10%. With 2% lime treatment the shear strength of 10% bentonite soil was increased to 0.27 kPa. Adding 10% lime to the 10% bentonite ultra-soft soil reduced the shear strength to 0.15 kPa. With 10% polymer treatment, the shear strength was increased by 45 times to 6.8 kPa for the 10% bentonite ultra-soft soil. The CIGMAT miniature penetrometer penetration varied linearly with the shear strength of the untreated ultra-soft clay soils and treated ultra-soft clay soils with 10% bentonite. pH was almost constant for untreated ultra-soft clay soils while it increased by 22% and 35% for the 10% lime and 10% polymer treated ultra-soft clay soilss respectively. Relative electrical resistivity decreased by 246% when the bentonite content was increased from 2 to 10% in the ultra-soft clay soils. Addition of 10% of lime to the ultra-soft clay soil with 10% of bentonite content decreased the relative electrical resistivity by 171%. Addition of 10% of polymer to the ultra-soft clay soil with 10% of bentonite content reduced the relative electrical resistivity by 545%. Power law, linear and Vipulanandan correlation models were used to predict the shear strength-resistivity relationship for the untreated, lime-treated and polymer-treated ultra-soft clay soils respectively. In addition, linear model was used to predict the water content relationship with electrical resistivity for the untreated and treated ultra-soft clay soils. The CIGMAT miniature penetrometer was modeled using 3-D axisymmetric finite element method, which predicted the penetration of CIGMAT penetrometer that agreed well with the experimental results of the untreated and treated ultra-soft clay soils. The CIGMAT miniature penetrometer penetration and the electrical resisitivity monitoring are two non-destructive methods that can be easily adopted in the field and the property correlations can be used to determine the shear strength of the ultra-soft caly soils in the field.

Pakistanandrsquo;s Gawadar Port: Benefits to Pakistan and China and its economic viability

Pakistan is located at the center of the Indian Ocean, making it a coastal state. It executes 95 percent of its trade through blue, via its ports in Karachi and Gwadar. Gwadar Port is the mega project of ongoing developmental projects in Balochistan which is shaping the economy of the World. The port is creating opportunities and possibilities for promoting regional and international shipping and it will resuscitate trade links between China and CARs being the closest route to warm waters. Gwadar Port has a vast region to influence; stretching up to several breakaway states of the former Soviet Union in the north, to Iran, the Gulf, the Middle East, and East Africa in the west, to India and Sri Lanka in the south. Moreover, this deep port is serving the Gulf and East African ports with fast feeder services. It has a deep-water sea complementary to Karachi and Bin Qasim ports for enhancing cargo shipments and therefore it will be a mother port for Asia in the coming years. It is argued that Gwadar Port has enormous potential to benefit China and Pakistan and also have the potential for uplifting Pakistan’s economy.

Wave energy assessment under climate change through artificial intelligence

The implementation of renewable energies is among the main challenges that we are confronting in the present situation of climate change. In this work, an artificial neural network (ANN) is optimized and used to assess the wave energy resource available to a wave farm over its service life. We select as case study a stretch of coastline in southern Spain. Different ANN architectures and training algorithms are tested for a dataset in deep water composed by: three values of significant wave height, four values of peak period, two values of incoming wave direction, three astronomical tide values, three storm surge values and three values of sea level rise induced by climate change. These deep-water sea states were propagated using a numerical model (Delft3D-Wave) and results were obtained at 176 locations. Thus, more than 114,000 data were used to train and test the ANNs. Once validated, the ANN was used to assess the cumulative wave energy at 704 locations during a 25-year period for three scenarios of rise in sea level according to the Intergovernmental Panel on Climate Change (IPCC) reports: present situation, pessimistic IPCC projection and optimistic IPCC projection. According to the results, the cumulative wave energy in the case study increases with increasing water depths. The greatest values of cumulative wave energy are reached at great depths off a shoreline horn and a port. Importantly, the rise in sea level will induce an increase in the wave energy resource. The ANN developed in this work allows the quantification of wave energy over long-term periods, reducing the computational cost, as well as the choice of the best locations for wave farms considering the effects of climate change.

Preliminary Design and Performance Assessment of an Underwater Compressed Air Energy Storage System for Wind Power Balancing

Abstract A key approach to large renewable power management is based on implementing storage technologies, including batteries, power-to-gas, and compressed air energy storage (CAES). This work presents the preliminary design and performance assessment of an innovative type of CAES, based on underwater compressed air energy storage (UW-CAES) volumes and intended for installation in the proximity of deep-water seas or lakes. The UW-CAES works with constant hydrostatic pressure storage and variable volumes. The proposed system is adiabatic, not using any fuel to increase the air temperature before expansion; a sufficient turbine inlet temperature (TIT) is instead obtained through a thermal energy storage (TES) system which recovers the compression heat. The system includes (i) a set of turbomachines (modular multistage compressor, with partial intercooling; expansion turbine); (ii) a TES system with different temperature levels designed to recover a large fraction of the compression heat, allowing the subsequent heating of air prior to the expansion phase; (iii) an underwater modular compressed air storage, conceived as a network of rigid but open tanks lying on the seabed and allowing a variable-volume and constant pressure operation. The compressor operates at variable loads, following an oscillating renewable power input, according to strategies oriented to improve the overall system dispatchability; the expander can be designed to work either at full load, thanks to the stability of the air flowrate and of the TIT guaranteed by the thermal storage, or at variable load. This paper first discusses in detail the sizing and off-design characterization of the overall system; then it simulates a case study where the UW-CAES is coupled to a wind farm for peak shaving and dispatchability enhancement, evaluating the impact of a realistic power input on performances and plant flexibility. Although the assessment shall be considered preliminary, it is shown that round-trip efficiency (RTE) in the range of 75–80% can be obtained depending on the compressor section configuration, making the UW-CAES a promising technology compared to electrochemical and pumped-hydrostorage systems. The technology is also applied to perform peak-shaving of the electricity production from an off-shore wind farm; annual simulations, based on realistic wind data and considering part-load operation, result in global RTE around 75% with a 10–15% reduction in the average unplanned energy injection in the electric grid. The investigated case study provides an example of the potential of this system in providing power output peak shaving when coupled with an intermittent and nonpredictable energy source.

Theoretical and experimental investigations of wave field around vessel in shallow water

Un-running vessel at the shallow-water road anchorage is under exposure to waves that come at arbitrary angle from the high sea. 3D waves from deep-sea area become practically 2D when entering shallow water. While mean periods are kept, waves become shorter and their crests become higher and sharpener than for deep-water ones. As a result of diffraction of waves that come from the deep-water sea at the vessel, a transformation zone appears where waves become 3D again. Dimensions of the waves’ transformation zone, character and height of waves in this zone specify safety of auxiliary crafts, e.g. tugboats, bunker vessels, pilot and road crafts, oil garbage collectors and boom crafts. In the complex 3D waves the trajectory of auxiliary vessel’s movement has to be safe, vessel’s motions have to be moderate. Besides waves’ height is one of the parameters that are used for forecast of movement of spilled oil. Last years the biggest part examination of waves’ problems was devoted to estimation of waves’ impact onto stationary or floating shelf facilities. For validity estimation, waves’ characteristics defined due to different theories, are compared with experimental ones. But characteristics of the waves around shelf facilities are hardly able to be compared to same ones of waves around bodies with vessel-type shape. At the experiments with vessels’ models, waves’ impact onto vessel was examined, but not the transformation of the waves themselves. So, comparing of waves area’s characteristics defined by both theoretical experimental ways is an actual problem. Aim of the paper is verification of results of wave area investigation; wave area is located around a vessel that is exposed of arbitrary angle waves at shallow water conditions. Description of experimental investigations of transformed waves in the towing tank is done; transformation zone appears around vessel’s model while running waves diffract on it. Distribution of waves’ amplitudes at the designated points was fixed by the special designed and manufactured unit. Experimental data is compared with computation results both of linear and non-linear theories. It was assumed that experimental results and theoretical data satisfactory meet each other; also that non-linear computations define the maximal values of waves’ amplitudes at all cases.

MEAN CLIMATIC PARAMETERS OF THE UPPER MIXED LAYER IN THE BERING SEA (LOWER BOUNDARY, TEMPERATURE, SALINITY) AND THEIR ANNUAL VARIABILITY

All available deep-water oceanographic data obtained in the Bering Sea in 1929–2019 are analyzed (101,425 oceanographic stations). Lower boundary of the upper mixed layer is determined from the vertical temperature profiles using the criterion of temperature deflection from SST (10 % for June-October and 0.2, 0.3, and 0.5 o С for November-May). The mixed layer is rather thin in June-September, its thickness is 10–20 m over the major part of the sea, and 30–40 m at the straits between central Aleutian Islands. In DecemberMarch, the mixed layer depth increases to 120–160 m in the northern deep-water sea and up to 180–200 m at the straits between central and eastern Aleutian Islands, though it is thinner in plumes of warm waters entering from the Pacific. At the continental shelf, the mixed layer can be traced to the depth of 20–40 m in the eastern Bering Sea and 60–80 m at Kamchatka in December-January and to 60–80 m in the eastern Bering Sea and 80–100 m at Kamchatka in February-March. The mixed layer temperature distribution is distinguished by two completely different seasonal patterns. The winter distribution pattern with the highest temperature in the areas adjacent to the Aleutian Straits is typical for November-June. The summer pattern with high temperature in the Karaginsky Bay, Bristol Bay, and Norton Sound and lower temperature near the Aleutian Straits is typical for July-October. On the contrary, the salinity distribution pattern is stable, with the highest salinity at the central and eastern Aleutian Straits and lower salinity in the coastal zone as the Anadyr Bay and Norton Sound influenced by the river runoff.

CONDITIONS FOR PRIMARY PRODUCTION OF PHYTOPLANKTON IN THE VOSTOK BAY (JAPAN SEA) IN SPRING 2016

The Vostok Bay was surveyed on March 16–18, 2016 with measuring of water properties profiles by oceanographic sondes Sea-Bird SBE-19plus V2 and Rinko Profiler ASTD-102 with sensors of pressure, temperature, conductivity, turbidity, chlorophyll fluorescence, dissolved oxygen, and photosynthetically active radiation (PAR) and collecting of water samples by SBE-32 carousel sampler with 10 liter bottles for further measuring of nutrients (P, Si and N in forms of nitrate and ammonium) and chlorophyll a concentration and phyto- and zooplankton abundance and species composition. Assimilation number (Pb ) of phytoplankton was determined using the optical sensor of dissolved oxygen mounted on logger Rinko AR01-USB and primary production was calculated from the measured values of Pb , Chl a and PAR. Values of primary production ranged from 200 to 2100 mgC/(m2.day). The highest phytoplankton growth was detected at the depth of 8–10 m in the northern Vostok Bay and 10–16 m in its southern part. The total daily production of phytoplankton within the Bay was estimated as 12.5 tC. Species composition of phytoplankton was formed mainly by diatoms (Bacillariophyta) and dinophytes (Dinophyta). The highest biomass of raw phytoplankton was registered at the sea surface, whereas the highest values of chlorophyll concentration occurred mainly at the bottom of the bay. Species composition of zooplankton was typical for spring season, with domination of copepods presented mainly by neritic species; its biomass was in 12 times lower than the phytoplankton biomass, on average. There was concluded that photosynthetic activity of phytoplankton was limited by nitrate availability, therefore it was intensified by penetration of relatively cold, nitrogen-rich waters from the deep-water sea to the Vostok Bay.

Laboratory investigation of crest height statistics in intermediate water depths.

This paper concerns the statistical distribution of the crest heights associated with surface waves in intermediate water depths. The results of a new laboratory study are presented in which data generated in different experimental facilities are used to establish departures from commonly applied statistical distributions. Specifically, the effects of varying sea-state steepness, effective water depth and directional spread are investigated. Following an extensive validation of the experimental data, including direct comparisons to available field data, it is shown that the nonlinear amplification of crest heights above second-order theory observed in steep deep water sea states is equally appropriate to intermediate water depths. These nonlinear amplifications increase with the sea-state steepness and reduce with the directional spread. While the latter effect is undoubtedly important, the present data confirm that significant amplifications above second order (5-10%) are observed for realistic directional spreads. This is consistent with available field data. With further increases in the sea-state steepness, the dissipative effects of wave breaking act to reduce these nonlinear amplifications. While the competing mechanisms of nonlinear amplification and wave breaking are relevant to a full range of water depths, the relative importance of wave breaking increases as the effective water depth reduces.

Wax appearance and prevention in two-phase flow using the multi-solid and drift-flux model

Abstract Wax precipitation may lead to obstruction of pipelines generating significant economic losses. Oil reservoirs, especially in the deepwater sea, are found in extreme conditions of pressure and, during the fluid flow inside the pipelines, the fluid temperature may decrease due to heat transfer to the surrounding (seawater) and phase change, tending to deposit solid particles on the pipeline walls. Within this context, it is important to develop a model that calculates the WAT (wax appearance temperature) of a fluid with known composition and then determine the point where the first paraffin crystal will appear inside a pipeline. The objective here is to provide a two-phase flow model coupled with paraffin precipitation model to calculate WAT inside the pipeline. We used the Drift-Flux Model to describe the two-phase flow in steady state and the Multi-Solid Theory to calculate the WAT. The results for a paraffinic mixture of four components show that the effect of the pressure can be considered negligible on WAT calculation for low pressure systems ( 10 MPa). Analyzing the effect of the fluid composition, the larger the number of light compounds in the mixture, the smaller will be the WAT, at constant pressure. For two different cases, it was determined the point inside the pipeline where the solid particles may deposit. We proposed an algorithm to find the minimum inlet temperature such that does not occur wax precipitation along the pipeline. The algorithm was successfully applied to a case study and may be useful for defining operational conditions to prevent solid blockage of pipelines.

Deep-water sea anemone with a two-chromosome mitochondrial genome

Mitochondrial genome organization of sea anemones appears conserved among species and families, and is represented by a single circular DNA molecule of 17 to 21 kb. The mitochondrial gene content corresponds to the same 13 protein components of the oxidative phosphorylation (OxPhos) system as in vertebrates. Hallmarks, however, include a highly reduced tRNA gene repertoire and the presence of autocatalytic group I introns. Here we demonstrate that the mitochondrial genome of the deep-water sea anemone Protanthea simplex deviates significantly from that of other known sea anemones. The P. simplex mitochondrial genome contains a heavily scrambled order of genes that are coded on both DNA strands and organized along two circular mito-chromosomes, MCh-I and MCh-II. We found MCh-I to be representative of the prototypic sea anemone mitochondrial genome, encoding 12 OxPhos proteins, two ribosomal RNAs, two transfer RNAs, and a group I intron. In contrast, MCh-II was found to be a laterally transferred plasmid-like DNA carrying the conserved cytochrome oxidase II gene and a second allele of the small subunit ribosomal RNA gene.

Size metrics, longevity, and growth rates in Umbellula encrinus (Cnidaria: Pennatulacea) from the eastern Canadian Arctic.

Umbellula encrinus (Linnaeus, 1758) is a deep-water sea pen commonly found in the eastern Canadian Arctic. It can reach heights of >2 m, and it has often been caught as fishing bycatch. Here, we characterized abundance/density, size metrics, longevity, and growth rates of U. encrinus colonies from Baffin Bay (between Greenland and Canada). No prevalent size classes were identified at most locations, except for Jones Sound and Cape Dyer, where small-size colonies dominated. Average number of growth rings in the internal skeleton (axis) of the examined colonies ranged between 2 and 68, with a maximum of 75. A bomb-14C analysis yielded 14C curves comparable with those of other deep-water octocorals with annual ring formation. A trace element analysis of Mg/Ca, Sr/Ca, Ba/Ca, and Na/Ca yielded values oscillating along the axis radius, with the number of peaks and growth rings being comparable. Growth rates averaged 0.067 ± 0.015 mm year−1 (radial extension) and 4.5 ± 1.2 cm year−1 (linear extension), considering rings to be formed annually. Relationships between radial growth rates, depth, and surface salinity were weak but statistically significant. Umbellula encrinus is a long-lived species, vulnerable to various types of fishing gear, with a skeleton that stores biological and environmental information.

Validation of a FAST spar-type floating wind turbine numerical model with basin test data

Global development of the offshore wind energy is devoted to applying into deep water sea areas. Spar-type floating offshore wind turbine (FOWT) has been demonstrated as the most mature FOWT concept, which has been studied for the longest time by researchers among all of the FOWT concepts in the world. Due to its excellent hydrodynamic performance, spar-type FOWT is considered as the most suitable type applied in deep water and harsh sea environment conditions, which has a huge market application foreground in the future. As a consequent, investigation of the offshore wind energy requires the hydro-aero-elastic-servo simulation tools to predict the coupled complex behavior of the FOWT system. However, little validation work has been done by now in the public domain. Thus, the purpose of this paper is to validate the commonly used simulation tool, FAST (Fatigue, Aerodynamics, Structures, and Turbulence), by referring to published basin test data. Through in-depth analysis of its advantages and deficiencies, it provides a good reference for the further improvement of this floating wind turbine’s numerical simulation tool in the future.

Palaeobiogeographic context in the development of shallow-water late Viséan-early Bashkirian benthic foraminifers and calcareous algae in the Cantabrian Mountains (Spain)

The late Viséan to early Bashkirian shallow-water carbonate Valdediezma Platform in the Picos de Europa Province of the Cantabrian Zone, has been subdivided into eight microbiotic intervals by means of similarity clusters (using the Morisita coefficient). The most complete Viséan-Bashkirian interval is represented in the Valdediezma Valley – Jitu l'Escarandi –road to Tresviso, where only the Steshevian to lower part of the Protvian (middle Serpukhovian) is missing. This interval is better represented in the Pompedrei Bridge to La Hermida composite section, and also in the deeper water section at Vegas de Sotres. These intervals contain a succession from the Mikhailovian (upper Viséan) up to the Krasnopolyanian (lower Bashkirian).The assemblages of the Valdediezma Limestone show, comparatively, low similarity indices with the neighbouring basins in the collisional front in the western extremity of the Palaeotethys during the progression of the Variscan Orogeny. In this mobile belt, two domains are recognized; a western domain composed of outcrops in south-western Spain and in the Moroccan Meseta, and an eastern domain comprising basins located in southern France. Some basins, such as the Betic Cordillera, initially had more influence from the western domain, but later, during the late Serpukhovian, it is considered as being part of the eastern domain. The Valdediezma Platform foraminiferal and algal content is coincident with its location as an isolated platform, surrounded by deep-water seas, and with higher similarities with the eastern domain.Regional tectonic events are recognized from the late Viséan onward, and they are mostly masked by the overprint of latest Pennsylvanian events. Facies changes are commonly observed, particularly at the base of the intervals, suggesting that facies control is the most important factor controlling the assemblages. It is considered that eustatic sea-level changes exerted a certain control on the assemblages.

Morphology and composition of the internal axis in two morphologically contrasting deep-water sea pens (Cnidaria: Octocorallia)

ABSTRACTUmbellula encrinus Linnaeus, 1758 and Anthoptilum grandiflorum (Verrill, 1879) are two species of deep-water sea pens (Cnidaria: Octocorallia) commonly found in the Northwest Atlantic. These sea pens are frequently caught as fishing bycatch, but little is known about their biology. Here we characterise the internal skeleton (axis) of these two morphologically contrasting species, in terms of axis carbonate composition and proportion, morphology and metrics (i.e. cross-sectional area and weight) through gradients along their lengths. Using the conspicuous growth rings present in the axis of U. encrinus we also estimated intra-colonial variation in radial growth rates for this species. X-ray diffraction (XRD) analyses revealed that the carbonate portion of the axis is composed of magnesian calcite (Ca, Mg)CO3 in both species. On average, the axis is composed of 71% carbonate material in U. encrinus, and 65% carbonate in A. grandiflorum. The carbonate proportion was greatly reduced from base (71%) to tip (33%) in the axis of U. encrinus, while in A. grandiflorum changes were less abrupt (~6% difference from base to tip). In U. encrinus, the axis is quadrangular in shape through its whole length, twisting longitudinally. Twisting can occur in both clockwise and anti-clockwise directions. The axis of A. grandiflorum varied from elliptical near the base to cylindrical through most of the remaining length, with no twisting observed. Axes’ cross-sectional areas also decreased with distance from the base in both species, being the largest near the base. Estimated radial growth rates in U. encrinus were variable within a single colony, ranging between 0.04 and 0.08 mm.yr−1. This is the first study to describe changes along the axes of sea pens, and to characterise the axes in the studied species. It provides a baseline for studies considering sea pens’ skeletons (e.g. ocean acidification and palaeoceanography).

Petroleum Distribution Characteristics of the Americas and the Exploration Prospect Analysis

AbstractThe world's present demand for oil and gas is still in a rapid growth period, and traditional oil and gas resources account for more than 60% of the global oil and gas supply. The Americas is the world's second largest production and consumption center of liquid fuel, and is also the world's largest natural gas producer. In 2016, the Americas had 85.3 billion tons of proven oil reserves and 18.7 trillion m3 of proven natural gas reserves, which account for 35.4% and 10.0% of world's total reserves, respectively. It produced 1267.1 Mt of oil and 1125.4 billion m3 of natural gas, which account for 28.9% and 31.7% of the world's total production, respectively. The crude oil and natural gas reserves are mainly distributed in the U.S., Canada and Venezuela. The U.S. is the earliest and most successful country in shale gas exploration and development, and its shale gas is concentrated in the southern, central and eastern U.S., including the Marcellcus shale, Barnett shale, EagleFord shale, Bakken shale, Fayettevis shale, Haynsvill shale, Woodford shale and Monterey/Santos shale. The potential oil and gas resources in the Americas are mainly concentrated in the anticline and stratigraphic traps in the Middle‐Upper Jurassic slope deposition of the North Slope Basin, the Paleozoic Madsion group dolomite and limestone in the Williston Basin, dominant stratigraphic traps and few structural traps in the Western Canada Sedimentary Basin, the Eocene structural‐stratigraphic hydrocarbon combination, structural‐unconformity traps and structural hydrocarbon combination, and the Upper Miocene stratigraphic‐structural hydrocarbon combination in the Maracaibo Basin of Venezuela, the stratigraphic‐structural traps and fault horst, tilting faulted blocks and anticlines related to subsalt structure and basement activity in the Campos Basin, the subsalt central low‐uplift belt and supra‐salt central low‐uplift belt in the Santos Basin of Brazil, and the structural‐stratigraphic traps in the Neuquen Basin of Argentina. In addition, the breakthrough of seismic subsalt imaging technology makes the subsalt deepwater sea area of eastern Barzil an important oil and gas potential area.